Within the past 5 years, a plethora of developmental research has been done on the genes responsible for initiating, patterning and proliferating the limb. Amazingly enough, it turns out that these limb patterning genes are conserved across phyla- from beetles to frogs, mice and even humans. The ubiquitous nature of these genes is startling and has suggested various scenarios for the evolution of limb morphology. However, such ideas are difficult to reconcile with the fact that although these limb patterning genes seem to be conserved across taxa, it is evident that the actual shape and structure of the beetle, frog, mouse and human limbs are inherently different. How could the same genes be patterning such diverse limbs? One hypothesis is that divergent gene functions, or variations in how conserved genes are regulated, could lead to diverse limb morphologies. One approach to testing this idea is to seek out closely related organisms with differing limb structure (i.e. the arthropods). This would allow for a direct comparison of the multiple components of regulatory pathways that lead to limb development in these organisms, and subsequently search for changes in gene regulation that correlate with their varying limb morphologies. This type of analysis is an expansive and challenging project, which will require the use of many different molecular, biochemical and genetic techniques to accomplish the following goals: 10 isolating and sequencing homologues of conserved limb patterning genes involved in setting up the limb axes in two closely related arthropods with different limb morphologies: designing primers, PCR, sequence analysis; 2) localizing the expression of transcripts involved in patterning the limbs of these arthropods: this will allow for a direct comparison of gene products- are they being expressed differently, the same? whole mount in situ hybridization; 3) looking for any spatial or temporal overlapping domains of expression in these arthropods with varying limb morphology: double and triple labeling studies, in situ hybridized sections.